The present invention relates generally to the field of ultraviolet radiation detection, and more particularly to sunscreen effectiveness monitoring.
Ultraviolet (UV) light is electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UVA radiation has a wavelength between 315 and 400 nm, while UVB radiation has a wavelength between 280 and 315 nm. While UVB radiation is mostly absorbed by the earth's ozone layer, UVA radiation is not. All bands of UV radiation damage collagen fibers and accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage. Overexposure to UVB radiation not only can cause sunburn, but also some forms of skin cancer. However, the degree of redness, generally not caused by UVA, does not predict the long-term effects of UV.
Sunscreen is a lotion, spray, gel, or other topical product which absorbs or reflects some of the sun's UV radiation and thus helps protect against sunburn when applied to skin. A sun protection factor (SPF) rating is a measure of the fraction of sunburn-producing UV rays that reach the skin. For example, “SPF 15” means that 1/15th of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of two milligrams per square centimeter (mg/cm2). A user can determine the effectiveness of a sunscreen by multiplying the SPF factor by the length of time it takes for the user to suffer a burn without sunscreen. Thus, if a person develops a sunburn in ten minutes when not wearing a sunscreen, the same person in the same intensity of sunlight will avoid sunburn for 150 minutes if wearing a sunscreen with an SPF of 15. It is important to note that sunscreens with higher SPF do not last or remain effective on the skin any longer than lower SPF and must be continually reapplied as directed.